The following patent publications and articles are believed to represent the current state of the art:
U.S. Published Patent Application Nos. 2008/0076474 and 2008/0277483;
European Published Patent Application No. 1 914 828;
China Published Patent Application Nos. 101303746 and 101520836;
A press release by Zenius Solutions: “Zenius Solutions enables interactive NFC on current GSM phones”, Oct. 19, 2009;
“Bladox Waver” by Bladox® (http://www.bladox.com); and
“KingSub® duoPass® by Taisys (http://www.taisys.com).